This paper presents the state of the art about teachers' collective efficacy. This concept derives from Bandura's Social Cognitive Theory, who considers efficacy beliefs as the basis of human agency and describes four sources that support its development. Teachers' perceptions of collective efficacy are their judgments that the faculty as a whole can organize and execute the courses of action in the school required to have a positive effect on students. The article outlines the ways how to measure this construct and describes research results about its relationship to students’ achievement and teachers' individual self efficacy. Last, the relevance of this construct is discussed especially in the face of the present moment of Brazilian school.